Nutrient leaching loss, plant growth, and nutrient uptake of 4-week
(transplanting to sale) ground-cover species were investigated under a range
of leaching conditions and with different sources of a controlled- release
fertiliser (CRF), Osmocote NPK (3–4 month) (Osm). Osm was applied
pre-planting at a rate equivalent to 800 g N/m3 to
pots containing sand, and composted pinebark and hardwood sawdust medium that
had received nutrient amendment during formulation.
Two experiments were conducted in a glasshouse over summer–autumn where
irrigation treatments produced defined leachate volumes. In Expt 1, leachate
volumes of <5, 50, and 200 mL every 2 days each received an additional
single heavy leaching event of 400 mL after 1, 2, or 3 weeks. In Expt 2, the 3
leachate volumes were each fertilised with new Osm (a newly purchased Osm) or
old Osm (a 2-year-old source), where both of these sources contained
0.5–1.5% visibly damaged prills; and damaged Osm, where damaged
prills were used exclusively.
In both experiments, increasing leachate volume increased
(P < 0.001) leaching of N (nitrate + ammonium),
P, K, Ca, and Mg. In Expt 1, leaching was highest (P
< 0.01) when the heavy leaching event occurred after 2 or 3 weeks for N and
after 2 weeks for P. When damaged Osm was used, N, P, and K loss was
3–15 times higher (P < 0.001) than from new and
old Osm (98.5–99.5% undamaged). The highest leaching loss of N,
P, K, Ca, and Mg occurred in the first week after potting up, with damaged
prills at highest leaching volume.
Increasing leachate volume (in the presence of a heavy leaching event) reduced
(P < 0.001) electrical conductivity (EC) of potting
medium after 4 weeks from 1.02 to 0.54 dS/m. Damaged prills reduced
(P < 0.001) EC at the high leachate volume in
relation to new Osm (2.38 v. 0.29 dS/m).
Treatments that increased (P < 0.05) nutrient
leaching generally reduced (P < 0.05) nutrient
concentrations in shoots and depressed the growth of some plant species. Shoot
growth of 2 of 5 species was reduced (P < 0.001) at
the highest leachate volume with an additional heavy leaching event in Week 1
or 2, and root growth of all but the slowest growing species declined with
increasing leachate volume. Damaged prills reduced (P
< 0.001) shoot growth of 2 of the 5 ground-cover species.
This study demonstrated that excessive leaching and the use of damaged prills
for containerised nursery plants fertilised with CRF results in high nutrient
loss, low residual nutrient content, reduced nutrient uptake in shoots, and
reduced shoot growth of some species.
Nutrient cycling in a RRIM 600 clone rubber plantation
